We have identified a neutrophil granule protein cathepsin G as a novel human cell-derived of chemotactic agonist for the formylpeptide receptor FPR (Sun et al. J Immunol. 2005). This is a significant advance in the understanding of the pathophysiological role of FPR in host defense and wound healing processes since cathepsin G is able to kill the bacteria and also promotes the healing of the wound.We have identified key fragments in the formylpeptide receptors that determine their specificity for ligand interaction. This provides structural basis for the design of synthetic agonists or antagonists for anti-bacterial and anti-inflammatory drug develpment studies.